HTTP multipart requests: Why do file fields become arrays while text fields keep only the last value

Repeated file fields are collected into an array, while repeated non-file fields appear to be collapsed, with only the last value retained. I find this somewhat counter-intuitive because both fields are appended using the same FormData.append() mechanism. Is this intended behaviour?

// TODO: should be parametrized if used as global workflow
const formData = new FormData();

for (const { mimeType = "application/octet-stream", binary } of files) {
  formData.append("files", new Blob([binary], { type: mimeType })); // results in [{s3: string}, {s3: string}, ...]
  formData.append("documentTypes", documentTypeId); // results in string; only last value will be accepted
}

return formData;

// TODO: should be parametrized if used as global workflow
const formData = new FormData();

for (const { mimeType = "application/octet-stream", binary } of files) {
  formData.append("files", new Blob([binary], { type: mimeType })); // results in [{s3: string}, {s3: string}, ...]
  formData.append("documentTypes", documentTypeId); // results in string; only last value will be accepted
}

return formData;

following formdata:

[
  {
    "name": "files",
    "value": {
      "binary": ...
    }
  },
  {
    "name": "documentTypes",
    "value": "47"
  },
  {
    "name": "files",
    "value": {
      "binary": ...
    }
  },
  {
    "name": "documentTypes",
    "value": "47"
  }
]

[
  {
    "name": "files",
    "value": {
      "binary": ...
    }
  },
  {
    "name": "documentTypes",
    "value": "47"
  },
  {
    "name": "files",
    "value": {
      "binary": ...
    }
  },
  {
    "name": "documentTypes",
    "value": "47"
  }
]

is apparently received as this:

{
  "files": [
    { "s3": "..." },
    { "s3": "..." }
  ],
  "documentTypes": "47"
}

{
  "files": [
    { "s3": "..." },
    { "s3": "..." }
  ],
  "documentTypes": "47"
}

Windmill•4w ago•

3 replies

Aron

HTTP multipart requests: Why do file fields become arrays while text fields keep only the last value

// TODO: should be parametrized if used as global workflow
const formData = new FormData();

for (const { mimeType = "application/octet-stream", binary } of files) {
  formData.append("files", new Blob([binary], { type: mimeType })); // results in [{s3: string}, {s3: string}, ...]
  formData.append("documentTypes", documentTypeId); // results in string; only last value will be accepted
}

return formData;

// TODO: should be parametrized if used as global workflow
const formData = new FormData();

for (const { mimeType = "application/octet-stream", binary } of files) {
  formData.append("files", new Blob([binary], { type: mimeType })); // results in [{s3: string}, {s3: string}, ...]
  formData.append("documentTypes", documentTypeId); // results in string; only last value will be accepted
}

return formData;

following formdata:

[
  {
    "name": "files",
    "value": {
      "binary": ...
    }
  },
  {
    "name": "documentTypes",
    "value": "47"
  },
  {
    "name": "files",
    "value": {
      "binary": ...
    }
  },
  {
    "name": "documentTypes",
    "value": "47"
  }
]

[
  {
    "name": "files",
    "value": {
      "binary": ...
    }
  },
  {
    "name": "documentTypes",
    "value": "47"
  },
  {
    "name": "files",
    "value": {
      "binary": ...
    }
  },
  {
    "name": "documentTypes",
    "value": "47"
  }
]

is apparently received as this:

{
  "files": [
    { "s3": "..." },
    { "s3": "..." }
  ],
  "documentTypes": "47"
}

{
  "files": [
    { "s3": "..." },
    { "s3": "..." }
  ],
  "documentTypes": "47"
}

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HTTP multipart requests: Why do file fields become arrays while text fields keep only the last value

HTTP multipart requests: Why do file fields become arrays while text fields keep only the last value

Continue the conversation

Windmill

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